Rashi and Rashbam: It is an expression of counting (or appointing). When Pharaoh counts (or appoints) his other servants to serve him during the party, he will also count the butler among them.

Targum Yonasan: 'Pharaoh will (remember you, and) elevate you honorably....'

Seforno: It implies the time when he had served Pharaoh as his personal butler, prior to his appointment to the position of chief butler. This was an indication of the deep affection that Pharaoh had for him, and was a sign that he accepted him back with open arms.