There is no sharp line separating the present-day philosophy of language from linguistics. Some of the theories developed by the philosophers of language, over the last hundred years or so, can illuminate many specific problems concerning English language and usage. The questions that concern application of such philosophical theories to specific problems of English language should thus be welcomed here, and, in fact, have been welcomed.
On the other hand, the questions that concern the theories of the philosophy of language in the abstract (the questions that could be asked about any language), are probably better asked at some other site, such as the Philosophy Stack Exchange.
For example, a question that involves the application of Gricean maxims to a particular locution is probably within the scope of this site. On the other hand, a question that calls for an interpretation of Heidegger's thesis that the language is the house of being would be off topic here.
It should be noted the questioners may not be aware whether their questions involve philosophy of language. The questioner may sometimes be simply puzzled by some feature of the language, and it is only in answering it that the philosophical undercurrents of that puzzlement become explicit. For example, the questioner may have never heard of Gricean maxims, but they may turn out to play the crucial role in a good answer to it.