Why did phoenicians become traders instead of farmers?

The Phoenicians became traders and not farmers because there were not many lands for them to farm.

At the beginning, they mostly traded with the Greeks: woods, wool, cotton, slaves, glass and a powdered Tyrian purple dye used by the greeks to color robes and dresses. To Egyptians, Phoenicians sold wine and bought Nubian gold from them. They obtained other materials (focusing on silver) from Sardinia and the Iberian Peninsula.

food chain i would say only because there is competition on getting food and survival

the lachish letters were written by hoshaiah, a military officer stationed possibly in mareshah,   and sent to yaush, possibly the commanding officer at lachish.

the series of letters were written in carbon ink in ancient hebrew on clay ostraca, shortly before lachish fell to the babylonian army of king nebuchadnezzar in 588/6 bc during the reign of zedekiah, king of judah.