Probably not, but you may have some workarounds.
First, keep in mind that the Assistant is meant to be multi-platform with a voice focus. Although it has a screen and touch controls, it is meant to be used by voice. Even with touch controls, these aren't guaranteed to be on a phone - Smart Displays will likely have these controls, yet not be able to make phone calls.
That said, you may be able to display a Basic Card that includes a link. This link could be to a tel:
URL which contains the telephone number and, on appropriate devices, would make the call.
I would have also suggested a Link-Out Suggestion, but the documentation for that seems to suggest that the Android Intent you trigger needs to be one that you have control over.