Apartment owners can see the evidence of a slower rental market.  More "move in specials" banners, concessions, for rent signs and stabilized rent are all evidence.  The Tribune has a more detailed article.

In the last few years rents had to go up, not only because the cost of properties, taxes, insurance have gone up, but the supply was lowered by condo conversions. 

Some of those condo conversions have reverted back to rentals.  In addition several new complexes have come online.

Though, as the article states, 3.5% increase this year is not too bad.  On an $800 apartment that is $28.00 more per month. 

Apartments in good neighborhoods in North Central Phoenix (Uptown Phoenix) and Central Phoenix as a whole had a greater than average increase and will continue to increase because this are is developing quickly and is close to major employment centers.  If these are kept up well and in good condition, then vacancy should remain low.