I phoned my wife and slept for two hours

lists the two activities done, while

I phoned my wife, and I slept for two hours

joins two related complete sentences using an optional joining comma and and.

I would not write

I phoned my wife, and slept for two hours.

Structurally, there are two different ways to write things.

I phoned my wife and slept for two hours

lists the two activities done in the form of A and B, while

I phoned my wife, and I slept for two hours

joins two related complete sentences using an optional joining comma and and so that we do not write them separately.

I would not write

*I phoned my wife, and slept for two hours.