With the proposed Biden infrastructure bill released, Amtrak has put forward their own proposal of expanded routes they could do were Congress to provide the funding. Notably, it would connect Phoenix to an Amtrak line, something not done since Amtrak rerouted service to a more southern route in 1996. Today, the closest Amtrak stop is in the town of Maricopa.

At present there is no passenger rail service between Phoenix and Tucson. Phoenix remains the largest city in the US with no Amtrak service and the largest city with no railroad mainline.
For some time now, the idea of a Phoenix to Tucson passenger rail service has been kicked around. The Arizona Department of Transportation has carried out environmental studies, looking at routes that would run alongside the I-10 freeway.
Funding remains an issue. The Arizona constitution only allows transit funding to be used for highways and not for railroads. Political willpower remains an issue as well, elected officials seem pretty focused on just expanding highways.
We could continue to sink money into highway widening, which research shows is ineffective and doesn’t serve as a long-term solution to traffic. Or we could instead choose to link our two major metro areas by passenger rail, getting cars off the road and reducing traffic.
An ADOT study found that even the planned I-10 highway expansion will not have the capacity to meet the expected growth and demand by 2035. Even if did want to keep adding lanes, there are sections of the I-10 the study says that simply cannot be expanded.
We need to create another transit option. Frequent passenger rail between Phoenix and Tucson could reduce traffic and provide a fast growing corridor with a choice that makes more sense than driving or flying and is far more environmentally sound.