Boxer Marvin Jones -- Dropping My Cell Phone in the Ring Cost Me the Fight!

It seems like a joke to everyone who saw it -- 'cause it was hysterical -- but boxer Marvin "Papi Gallo" Jones says dropping his cell phone from his trunks during a fight ... cost him the bout!

Jones was fighting Friday night in Florida when his cell phone -- yes, cell phone -- fell onto the mat right after the opening bell.

Jones tells TMZ Sports he was listening to music before the fight and tucked the phone into his shorts. When he headed to the ring, he pulled out his headphones ... but not the phone. Next thing ya know his Samsung Galaxy's taking a standing 8.

Jones says he lost as result of the blunder because it threw off his focus. He says he kept thinking, "Man, my cell phone just fell out in the ring – and on TV!"