Windows in Phoenix are a west-elevation problem before they are a style problem. Glass facing the afternoon sun loads a room faster than the cooling system can recover, and the night often stays warm enough that the glass never really resets. Aluminum single-pane windows in older Maryvale, Sunnyslope, and central houses are still common. Newer tracts have dual panes whose seals fail, leaving a fog that will not wipe off. Stucco joints at the sill crack, dust packs the track, and the first hard monsoon rain comes through a gap you ignored in May.
Name the failure. Fog in the pane, a frame that is soft, a lock that will not catch, or heat you can feel from the sofa are different jobs. One living-room slider is not a whole-house replacement. A bedroom you cannot use after two in the afternoon might be. Say how many openings and which way they face. Say whether the frame is aluminum, vinyl, or wood. Wood is the surprise in a few older central houses and it swells and rots differently than aluminum.
Ask whether the proposal is an insert that leaves the old frame or a full-frame opening that lets the flashing meet the weather barrier. Inserts are a poor idea when the sill is already soft from a stucco leak. Ask who patches stucco and interior drywall. Ask how the new sill sheds water so monsoon rain does not sit in the track. Ask about the gap around the frame and what fills it. Dust infiltration on a haboob day is a sealing question, not a reason to replace every opening by default.
Do not turn the call into a promise about the electric bill. Turn it into a count, a direction, and a condition. West glass in this city is a comfort and a durability question because the heat does not let up after sunset. A north window on the same house may only need hardware. Say the difference. Call the number on this page.