The national housing slowdown is spreading to markets like Las Vegas and Phoenix, where prices still haven’t reclaimed their pre-crisis peaks.

After home values rose sharply this year, the market has shifted in recent weeks. Prices fell slightly in November while the inventory of unsold homes in the Las Vegas region has roughly doubled compared with a year earlier, according to the Greater Las Vegas Association of Realtors. Existing home sales slowed nearly 12% in November compared with a year earlier.

Angela...