The Phoenix Transit app is available for both iOS and Android platforms and is available in both free (ad-supported) and paid versions. The iOS free version has an in-app purchase that lets you remove the ads.
The application has the data available from the Valley Metro Transit system for both the Bus and Light Rail systems. This data includes route, trip and stop time information for the buses and light rail trains.
There are 3 main screens available. The first screen shows the list of stops available on a particular route. There is a selection button available that lets you pick which route you are interested in seeing. If a route goes two directions (say Eastbound and Westbound), you can also switch directions. The alternate direction might have a different set of stations.
The second screen shows all the stop times available for that station on that route. This is important to note, since the same station might be used on several routes, the times shown are only for the selected route. This will let you select what time you need to be at the particular station to catch the bus or light rail.
The third screen shows the stop times for all the stations on the route for the trip selected. So you can determine when you will need to get off at your exit station. You can also use this to select what time you need to be off the bus or light rail at a particular exit and work backwards to determine what time you need to be at the entry station.
Important Note: Route and arrival data provided by permission of Valley Metro.