Yes, he is the author of the dialogues, but he never speaks in his own name. When we read Plato we only know what his Socrates and Glaucon and others say. He let’s us know that he is present in some of the dialogues, but he never says anything. I would think when he was actually with Socrates he was not always silent. So why is he silent in the dialogues?I don't understand why you say Plato never says anything. It is not my argument that Plato speaks in the dialogues. However, it is he who writes and puts words into the mouths of the players.
It is not just a matter of his personal method or style. It is because philosophy is different than other branches of knowledge. It is not about doctrines or theories but a way of life and suitable only for those who are willing to live this way.There may well not be a treatise on Plato's philosophy written by him. This clearly is not his chosen method - but dialogue is.
In the Seventh Letter Plato says (Here he speaks in his own name. It is a private letter.):
It is thus, and in this mind, that such a student lives, occupied indeed in whatever occupations he may find himself, but always beyond all else cleaving fast to philosophy and to that mode of daily life which will best make him apt to learn and of retentive mind and able to reason within himself soberly; but the mode of life which is opposite to this he continually abhors. Those, on the other hand, who are in reality not philosophic, but superficially tinged by opinions,—like men whose bodies are sunburnt on the surface —when they see how many studies are required and how great labor,and how the orderly mode of daily life is that which befits the subject, they deem it difficult or impossible for themselves, and thus they become in fact incapable of pursuing it; while some of them persuade themselves that they have been sufficiently instructed in the whole subject and no longer require any further effort. (340d-341a)
… none, I say, of these will ever learn to the utmost possible extent the truth of virtue nor yet of vice. For in learning these objects it is necessary to learn at the same time both what is false and what is true of the whole of Existence,62 and that through the most diligent and prolonged investigation, as I said at the commencement; and it is by means of the examination of each of these objects, comparing one with another—names and definitions, visions and sense-perceptions,—proving them by kindly proofs and employing questionings and answerings that are void of envy—it is by such means, and hardly so, that there bursts out the light of intelligence and reason regarding each object in the mind of him who uses every effort of which mankind is capable.
And this is the reason why every serious man in dealing with really serious subjects carefully avoids writing, lest thereby he may possibly cast them as a prey to the envy and stupidity of the public. In one word, then, our conclusion must be that whenever one sees a man's written compositions—whether they be the laws of a legislator or anything else in any other form,—these are not his most serious works, if so be that the writer himself is serious: rather those works abide in the fairest region he possesses. (344b-c)