“To be just about to do something”

Definition:  You have the intention do something in the immediate future 

Example: Calling a friend on the phone 

Christina: “Hi Jake! I thought I’d come round for a coffee. Is it a good time for you?”

Jake: “Actually, I’m just about to leave for work ”

Christina: “Oh okay then, I’ll ring you tomorrow in that case”

Jake: “Good idea, I’ll speak to you tomorrow then ”