Questions & Answers about O prazer foi meu.
Foi is the past tense of ser (to be), so it means was.
That makes sense because this expression is usually said after an interaction, meeting, conversation, meal, etc. You are referring to the pleasure as something that has just happened.
Compare:
- O prazer é meu = The pleasure is mine
More immediate, also very common. - O prazer foi meu = The pleasure was mine
Looking back on the interaction that just happened.
In real Brazilian Portuguese, both are used, and both sound natural.