Sorry, but people are missing the point. In very hot weather the actual ground speed at which the airplane takes off is much higher than it is in cold weather. That is because air density is lower with either hot or high conditions. As a result the tires are very hot, because they're rotating at a much faster rate than in cooler conditions. As a result the landing gear is left down for a brief period to cool off other tires. Failing to do that could result in a tire blowing out after retracting the landing gear. This is rare, and in the US happens more often at PHX than anywhere else.

There is another thing that happens at PHX in the summer sometimes. Engines can only be started at temperatures for which there are published specifications. That is because turbine engines are at their hottest when being started. As a result some older aircraft must sit at PHX waiting for the temperatures to drop.

All this is normal, but very rare except at places like PHX, that have very, very hot summer temperatures, and others such as SLC and DEN which are very high as well.