P50 controller described an approach event when he/she mis-handled an IFR aircraft believing the aircraft was VFR; claiming recent time off may have contributed to the lack of vigilance.

Narrative

I sat down at a satellite sector (Pima) which was combined with Willy Sector. Working arrivals/departures and overflights. Cessnas and Pipers on this position are 'usually' VFR; conducting practice approaches. I vectored Aircraft X for his approach. I descended Aircraft X to 'maintain VFR at 3500'. I gave a heading to join; and a VFR approach clearance; specifically telling him to maintain VFR at all times. Aircraft X had these two opportunities to 'correct' me in my thinking that he was VFR. He didn't. I switched him to IWA Tower. I also modified the data block to a '3K' tag instead of an automated STARS transfer by flashing a 'hand off' to the tower. Because of this; IWA Tower was wondering if I gave Aircraft X an IFR approach clearance. I told them to give Aircraft X back to me. IWA Tower put Aircraft X back on my frequency. After apologizing; I issued a proper approach clearance and switched Aircraft X prior to IWA Class D. Recommendation; Don't ASSUME. I sat down and figured that Aircraft X was VFR because he is VFR 99% of the time. After being off for a while; one should be extra vigilant for slip ups. One needs to shake off the rust. My first position assigned was a different handoff position. In retrospect; it probably would have been better to put someone returning from an vacation back on a radar position with a handoff; just so the 'rust' could be knocked off while having another set of eyes watching the operation.