After he had told them that he was going, they understandably were dubious about their ability to continue without him (14:5).
Philip needed to have some proof. Jesus responds by asking him if he hadn't been paying attention. "Whoever has seen me has seen the Father. The words I speak are the Father's words."
By the words he had spoken, Jesus has revealed God to them.
He then adds "Even if you have trouble believing the words I say, just look at the works I have done. What I have done is evidence that I am in the Father and the Father is in me."
By the deeds he had performed, Jesus has revealed God to them.
In the small group that I am part of, the leader asks at the beginning of each meeting, "Where have you seen God?"