On what grounds did the supreme court claim it had a right to rule in the baker case?

Jack Phillips, a Colorado baker who refused to bake a cake for a same-sex wedding, was taken to the court by a transgender woman. The Supreme Court of Colorado found that he was discriminating against potential customers. However, he won the case arguing that baking a cake with sexual connotations was against his religious beliefs.

powers  are  denied  to the  national governmentin three distinct ways: some  powers, such as the  power  to levy duties on exports or prohibit the freedom of religion, speech, press, or assembly, are expressly  denied  to the  national government  in the  constitution.