What's the difference between call and call up to mean make a telephone call to? Is the latter any more informal than the former, or is it mainly a regional thing?
call someone or something up
To telephone someone or something: As soon as I heard the news, I called up my broker and told her to sell the stock. I called him up to ask if he was free for lunch.
The American Heritage® Dictionary of Phrasal Verbs
call someone up
(especially North American English) to make a telephone call to someone
call (someone) up or call up (someone)
chiefly US : to make a telephone call to (someone)
I haven't spoken to her in years, but I called her up last night and we talked for hours.
Call me up when you get back from your vacation.
I called up my doctor and made an appointment.
Best Answer
In the variations on U.S. English with which I am familiar, "call" and "call up" can be used interchangeably to describe placing a telephone call. They have little to no difference in meaning for that use, but they have different alternative meanings.
To "call" someone may also mean to shout to attract their attention, and especially to shout their name for that purpose. "I called him, but he did not hear me." It can also communicate the name I use for someone: "His given name is George, but I call him Pookie."
On the other hand, to "call up" can mean to summon a reserve or back up person to duty; this sense is most often used to describe returning military reservists to active duty, or to describe elevating athletes from lower-tier leagues to higher leagues.
You might prefer one of "call" or "call up" if the other presented a risk of confusion with one of its other meanings.