WHOLE CHARACTER
背bèi, bēi
the back (脊背); the reverse side; background (背景); with one's back to (背光); to recite from memory (背书); to violate (违背); unlucky (背运)
背 read bèi is the back of things; read bēi it is what you carry.
ZDIC: 形声; 北 the sound, the flesh-form 月 matching the body part.
SOUND
北běi
north
Standalone meaning is kept separate from its sound role in 背.
In 背: sound Sound side per ZDIC: běi shares 背's initial and final; only the tone differs (3 vs 4).
MEANING (THE FLESH FORM)
月yuè
moon; month
月 can be the moon/month source or a flesh-related form in other characters; the distinction is stated where relevant.
In 背: meaning (the flesh form) The 月 here is the flesh form, not the moon.