be rid of / get rid of

Be/Get rid of is not a phrasal verb. Rid is an idiomatic predicate (the past participle of the verb rid, rid, rid) that combines with an auxiliary be like other participle adjectives like tired or pleased, and indicates an object by way of a preposition.

• He finally got rid of that cold.
• He's pretty tired of hamburgers by now.
• He's quite pleased with the new dishwasher.

In the case of pleased the preposition is with; in the case of rid and tired, it's of.

That works for both stative be rid of and causative/inchoative get rid of. They both use of because they both use rid. The difference between be and get is the difference between a state and making the state come about. That's what "causative/inchoative" means.