The mid-century high-rises along Central Avenue in Phoenix – some with ash trays still dotting hallways – are transforming into collaborative and creative space for growing companies. Just a couple of years ago, it was decried that the lack of parking, small floorplates and low ceilings made the spaces in midtown Phoenix undesirable in light of growing demand for open, contiguous space. "I haven’t had one tenant looking at midtown towers ask me about parking until they’re ready to do the…