Is it unwise to get a recommendation for philosophy phd apps from a professor you had relatively early in college?
I don't have experience with philosophy, but I can't imagine this part of admissions is too different.  It's pretty common for students to have one or more letters from faculty they haven't had classes with in the past year, so no that's not a problem.  (In fact, sometimes it happens with all the letters, if the student takes time off--e.g., see: If you want to do a PhD in mathematics, how important is it to start immediately after finishing undergraduate studies? )  What's important is that each letter writer should have something meaningful to say about your preparation, talent, attitude, performance, work ethic, etc.  Also, depending on the circumstances, it may be very natural for you to continue to have plenty of interactions with this professor over the next year or so whether or not you take another class with her.

That said, you should get letters from some people you've taken in your 4th-5th year (particularly master's classes if possible).  The main reason for this is you want recommendations which can discuss your performance in more advanced classes, which is presumably what you'll be taking.