Leather products are impure (najis) and salãt in them is not permissible, if we know that they have been made from the hide of an animal not slaughtered according to Islamic laws. Such products are considered pure and salat in them is permissible, if there is a probability that they were made from skin of an animal that is essentially halãl and was slaughtered according to Islamic laws.
If leather thing or products and kept in the pocket then prayer is valid and in order because it is not your dress . Rules applies on dress.
Off course avoid wearing leather cloths because it creat problem at the time of the prayer because you can not say your prayer in it except if this leather is from Muslim country or you are aware that it was leather from halal animal and was slaughtered in an Islamic manner which called zabeeha.
Because there are conditions for the prayer and among those is purity of dress that it should be pak.
Syed Abul Qasim Rizvi