The UNITED STATES Constitution is not the Texas, Arizona, New Mexico Constitution - it is the CONSTITUTION OF THE UNITED STATES. .)Where in the constitution does the federal government derive the authority to do so? The first amendment prohibits the federal government from passing laws that restrict an individuals religious practices but it does not grant the federal government any authority over the States (looking at the text from a strict constructionist standpoint).
Exactly- which is why I am sure you agree with Obergefell and that a gay couple has a constitutional right to marry in Arizona.
Meanwhile- business's have an obligation to follow the law- which means in Phoenix, that regardless of the business owners religious beliefs that they cannot refuse to sell to blacks, Jews, women, Mexicans or gays.