Lawrence Phillips' biological mother -- and the people closest to him -- do not believe the ex-NFL star committed suicide in his prison cell ... with his next of kin telling TMZ Sports, "I know for a fact he wouldn't do that."
We spoke with Tonissa Murdock -- who was listed as Phillips' next of kin with Kern Valley State Prison due to their close relationship for more than 20 years.
Murdock says her family took Lawrence in the '90s and he's been like a brother to her ever since.