It is possible that the loudspeaker in the phone doesn't deliver the
same pitch at different angles, but it seems more likely that the ear
is a more closed resonator when the phone is right up to it, and more
open when it is tilted away.

The ear does keep growing as we age, so if this is the explanation,
in a few years you will hear G# and A# instead of A and A#.  You can
also try cupping your hand over the ear piece to see if you can get
the same effect.

John Nolte - continually amazed at what we notice that doesn't make
the 6 o'clock news.