What are some philosophical interpretations of the poem "Mending Wall"?

That is an interesting question to ask. In this context, I am interpreting "philosophical" to mean some timeless and universal meanings for Frost's "Mending Wall." The two that I take away after reading it are that we should tamper with nature only for some good purpose and that the structures created by humankind may interfere with relationships amongst people more than they aid them.
The first few lines of the poem tell us that nature does not like human-built barriers. The narrator says, "Something there is that doesn't love a wall" (line 1). That something is nature, which does its best to break up the wall with its cycles of freezing and warming. The narrator goes on to point out that, while there could be a purpose to building a wall, he clearly sees no such purpose in this situation.  Therefore, if we are going to build walls, or anything else, interfering with nature's natural course, we should do so only for a very good reason, to the benefit of someone or some ones. 
The narrator also sees that building can create a barrier and harm relationships:

Before I built a wall I'd ask to know
What I was walling in or walling out,
And to whom I was like to give offence (lines 32-35).

He understands that building a wall keeps people out as well as keeping something or someone in, and he sees that not having walls or other barriers might make for better neighbors than having walls. It is not too great a leap to infer from this that the narrator sees building upon the landscape as something potentially harmful to human relationships. If a structure is not enhancing our ability to get along with one another, perhaps it is a structure that should not be.