What does this mean?

"This consciousness turns back; it goes no further than name-and-form .... when there is consciousness with name-and-form as its condition, AND name-and-form with consciousness as its condition.
"paccudāvattati kho idaṃ viññāṇaṃ nāmarūpamhā na paraṃ gacchati .... nāmarūpapaccayā viññāṇaṃ; viññāṇapaccayā nāmarūpaṃ."
(SN 12.65)

Let's see first how consciousness is the condition for name-and-form. And then we"ll see how name-and-form becomes the condition for consciousness.

First of all, open this link in a new tab, and refer to it as the "big picture".

The process usually goes this way:

External stimulus from an external āyatana >> descent of the indriya in the internal āyatana >> sense-consciousness >> contact >> feeling >> perception >> thoughts & mental concretism (vitakka & vicāra) >> manosañcetanā >> maintenance of consciousness >> descent of consciousness in the nāmarūpa's khandhas >> descent of nāmarūpa in saḷāyatana (particularly the external ones) >> external stimulus from an external āyatana.

So on and so forth. Again and again.
And if, basically, one does not restrain the indriyāni, and therefore intends, plans, and have a tendency towards (ceteti -  pakappeti - anuseti - SN 12.39), this vicious circle "turns back" ; that is to say that it does not allow consciousness to reach the higher  nidānas, but instead, the all nāmarūpa shebang (in satta,) maintains consciousness - and consciousness has therefore name  & form as its condition.  (see fig.1 below).



Let's see what is said in the early suttas, (common to the early Buddhist schools (viz. with parallels)), about the above process.

When consciousness is established and has come to growth, there is a descent of name-and-form (in saḷāyatana).
Tasmiṃ patiṭṭhite viññāṇe virūḷhe nāmarūpassa avakkanti hoti.
(SN 12.39)


With name-and-form as condition, the six sense bases come to be.
Nāmarūpapaccayā saḷāyatanaṃ
(SN 12.39



Let's summarize what we have seen up to now, (backed up by suttas with parallels):

First, consciousness is the condition for nāmarūpa:
We have seen that, when consciousness is established and has come to growth, there is a descent of name-and-form. And that the six sense bases come to be.
Once in sāḷayatana, the forms and dhammas of the Nāma-Rūpa nidāna get "sensualized" in the external āyatanāni -  (saḷāyatana being the fields (aka sense-bases) of sensory experiences).
For instance, a guitar delivers a sensuous sound. Or a flower a sensuous smell, etc.

When the external āyatanāni reach the internal āyatanāni, there is a sense-consciousness - and this is called "contact (phasso). 

Phasso appears only in the definition of nāma, in the Nikāya suttas (e.g. SN 12.2). Not in the Chinese and Sanskrit texts. But there is no incompatibility in that.

It is important to understand that the definition of Nāma, in the Āgamas (SĀ 298), [the same than the Sanskrit Arv 5], and the definition in the Nikāyas (SN 12.2), are not conflictual.
In SĀ 298, Nāma = viññāṇa, saṅkhāra, vedanā and sañña (idem for Arv 5); while
In SN 12.2 Nāma = phasso, vedanā, sañña, cetanā and manasikāro.
It is just a matter of where you situate yourself, when analysing Nāma.
Are you in (saḷāyatana + satta,) the "world" of senses - or are you oustside the "world" of senses. (for an extensive definition of the Buddhist "world" see SN 35.82 (SĀ 231)).
Note: for instance we know that there are two feelings - the "outside of the world" feeling, in the saṅkhāra nidāna. And there is also the "inside the world (of senses)" feeling; that is to say, the feeling nidāna proper (in satta > see the "big picture" visual aid).

We started with consciousness as the condition for name-and-form, (When consciousness is established and has come to growth, there is a descent of name-and-form).
And up to now, we are still concerned with the "Nāma-Rūpa nidāna" part of the descent. The Nāma-Rūpa of the definition from the Āgama and the Sanskrit text. That is to say forms and dhammas from the Nāma-Rūpa nidāna (that get "sensualized") -  AND a consciousness khandha, from the Nāma-Rūpa nidāna, that changes to a sense-consciousness.

However, it is really the "Nikāya" style of Nāma-Rūpa, that will be responsible for making Nāma-Rūpa the condition for consciousness. That is to say: phasso, vedanā, sañña, cetanā and manasikāro (as per SN 12.2 definition of Nāma-Rūpa).
And we must wait that this "new" nāmarūpa leaves saḷāyatana to reach Satta proper.

Note also that the "contact" and "feeling" links, although still "sensorial" are not of the domain of saḷāyatana anymore; which makes the Nāma of the Nikāyas, definitely outside the range of saḷāyatana.

Let's see now how Nāma-Rūpa really becomes the condition for consciousness:
We know that clinging-khandhas, are an appropriation of Nāma-Rūpa nidāna's khandhas.
So we are still dealing with the same khandhas that are in the definition of Nāma-Rūpa nidāna's components in SĀ 298 and Arv 5. That is to say:  the form aggregate (khanda) affected by clinging, the feeling aggregate affected by clinging, the perception aggregate affected by clinging, the formations aggregate affected by clinging, and the consciousness aggregate affected by clinging (MN 23).
Might "affected by clinging" be better translated as: the "appropriated" aggregate (khandha) of form, etc.

When someone through contact (after a sense-consciousness), has felt and perceive a feeling from a form - and appropriated the three - making them clinging-khandhas - the suttas/sutras tell us that there are still synergies (saṅkhāras) under the form of cetanā (ceteti), and other devising ("mind-making" - manasikārā) things like planning (pakappeti), tendencies towards (anuseti), developments (papañcas), etc.

Let's see, for instance what intention (cetanā) does when combined with mano.
Note that intention (cetanā), is not the only factor that allows a support (basis-footing) for the maintenance (continuing of state = stay) of consciousness. But in the fig. 4 below, the thing is so obvious, that this particular instance is worth showing.
As I just said, other factors applies also; like in SN 22.54, where it is said that the feeling element, allows also a support for the maintenance of consciousness. 

So, it is said like below, (in SN 12.11 and SN 12.39,) that cetanā, combined with mano (manosañcetanā), does allow the maintenance of consciousness.

And that is just just how Nāma-Rūpa, becomes the condition for consciousness - A consciousness that has just to establish itself again in the Nāma-Rūpa nidanā.
Nāma-Rūpa, becomes the condition for consciousness, through the clinging (appropriated) khandhas (that is to say, the appropriated Āgamas khandhas  - AND as well, through the process of the the Nikayas' components; particularly the mano (manasi) part.