If it is something that is widely available to the public, yes, and yes you can call the president's office. They can email him, mail him, call and leave messages with his staff, contact him via facebook, twitter, reddit, and other social media.So if Trump allows some constituents to talk to him directly at Trump tower etc (which he does, generally large donors) he must allow everyone to?
That twitter may very well be about to end up classed as both.

The White House
President Donald J. Trump and Vice President JD Vance are committed to lowering costs for all Americans, securing our borders, unleashing American energy dominance, restoring peace through strength, and making all Americans safe and secure once again.

Trump is not allowed to prevent people from contacting him in any of these ways. If they are making threats or what not, that will be handled by secret service.