Is this sentence: "I was eating my dinner when the phone rang" both imperfect and perfect tense? "I was eating dinner" is imperfect tense and "when the phone rang" is perfect tense, right? Thanks! :)?
Yes your note is correct.
A perfect verb describes a finished action, so Past Simple tense (rang) is an example of a perfect verb.
An imperfect verb describes a long and unfinished action. Here such verb is was eating. The meaning of this phrase is that the person was in the middle of an action when speaking.