No, the word "was" can't be used as a prepositional phrase. Rather, it can be used as a linking verb or an auxiliary verb. Explanation: Click this link
No, the word "was" can't be used as a subordinating conjunction. Rather, it can be used as a linking verb or an auxiliary verb. Explanation: Click this link
Yes,the word "was" can't be used as a action verb.That is,the word was is not a action verb. But it can be used as a linking verb and a helping or auxiliary verb. Explanation: Click this link