This is very fascinating stuff, but it's not really that relevant for the question posed in the title. Our Latin letters got their shapes from the Greek alphabet, by way of Etruscan. Greek in turn is based on the Semitic abjads (consonantal alphabets) which in turn likely go back to Hieroglyphics. B comes from Beta, from Beth/Bayt in Semitic languages, going back to a Hieroglyph for "house". Of course beth also means house in Hebrew, as in Bethlehem.
This is not a mystery, and since the modern letters ultimately got their shapes from pictographic drawings, there is no real connection between shape and sound anymore. At most it may have influenced how the letters have been simplified over time.
This is not a mystery, and since the modern letters ultimately got their shapes from pictographic drawings, there is no real connection between shape and sound anymore. At most it may have influenced how the letters have been simplified over time.
https://en.wikipedia.org/wiki/Bet_(letter)