What does "What Primary Physical Custodian" mean with regards to child custody?

When we divorced 7 years ago, we were asked to complete a parenting plan. On it we checked JOINT for the "Legal custody shall be..." box and then MOTHER was checked for "The primary physical custodian shall be..." box. We have a 50-50 joint custody agreement and are schedule has us with the kids an exact and equal amount of time. However, just yesterday my ex was trying to convince me that she has more custodial rights, and thereby a greater say, in what happens with the kids because of that box relating to the primary physical custodian being her. I don't agree with her interpretation and am not entirely sure what it means. Any thoughts on this one?