Commercial speech is not protected under the 1st amendment. However, political and religious speech, which makes up most of the robocalls during the election season isn't covered.
That's not quite true. Restrictions on commercial speech are subject to intermediate scrutiny, whereas the default for most other restrictions speech is strict scrutiny. That's not nearly the same as totally unprotected, like obscenity for example.
It amazes me that this completely nonsensical distinction passed muster in the courts.
There is no meaningfuk distinction between political, commerce, and religion, and the First Amendment specifically prohibits granting special legal status to religious activity.