You can say 'It's a pleasure' or 'My pleasure' as a polite way of replying to someone who has just thanked you for doing something. 'Thanks for your call.'—'My pleasure.' Download our English Dictionary apps - available for both iOS and Android.
Pleasure means positive emotions, and mine means 'my'. When someone says "the pleasure is all mine" it is usually a comment made after.
I've heard a native English speaker say, "'It's my pleasure' is old "The pleasure was all mine" is particularly charming in some cases:D.