According to the police report ... a Philly cop identified as Officer Burnett says he noticed a pickup truck idling for 10-15 minutes at a gas station back in March, so police ran the plates and it came back to Jacob Giddings.

Cops say Giddings had an active warrant for assault, so Officer Burnett asked him to step out of the vehicle, and when he "started to resist" ...  Burnett used force to pull him out.

However, Burnett's body cam was activated, and as you can see ... it captured Giddings apparently recording the incident on his phone from inside his truck. That fact is not mentioned in the police report.

Based on Burnett's body cam, it looks like Giddings lost his phone in the struggle. Later, after Giddings was in custody, the officer picked up the phone and appeared to gain access to the footage. He hits a few commands, but it's not clear from the footage what he did.

Giddings, from the police car's backseat, is heard asking Burnett if the video is still on his phone, and the cop says he doesn't know -- but Giddings believes Burnett deleted the vid.

According to the police report, cops also found marijuana on Giddings and he was arrested and charged with one count of resisting arrest and one count of drug possession. During the bust he suffered minor cuts to his wrist from the handcuffs, and was taken to a hospital for treatment.

Giddings has lawyered up, and his attorney, Donte Mills of Mills &. Edwards LLP, tells TMZ ... they'll be suing Philadelphia PD for excessive force and assault, tampering with evidence, false arrest and malicious prosecution.

Mills says they later recovered Giddings' arrest video from his iCloud account. We're told Giddings is still being prosecuted, and he doesn’t believe Burnett has been disciplined.