The Republicans have been itching for a war with Iran. I think Bolton talked Trump into it.

Then, I think Trump changed his mind and backed away from the plan, enraging Bolton, causing him to quit.

Trump is an impulsive fool with the emotional intelligence of a sociopathic two year old. He is easily talked into something, then talked out of it by the next person he sees.

Pure speculation, but looking at what's been going on this summer, I guess the call was to Bibi and involved a promise to go to war with Iran.