Where does “ဖ” come from?

ဖ (Burmese) comes from Burmese ပိ — to be pressed, to be flattened, to be crushed.

Ancestry of “ဖ”, step by step

Step	Language	Word	Meaning
1	Burmese	ပိ	to be pressed, to be flattened, to be crushed

ဖ — Etymology, Origin & Word History | Etymology Explorer