When I can use the phrasal verb 'call out'?

[Samuel]

English Language Tests, Intermediate level

ESL/EFL Test #277 "My computer and me", question 3

As a result of this I find I have to call ......... experts to come and help me.

(a) out
(b) over
(c) about
(d) up

English Language Tests, Intermediate level

ESL/EFL Test #277 "My computer and me", answer 3

As a result of this I find I have to call up experts to come and help me.

Correct answer: (d) up

Your answer was: incorrect
As a result of this I find I have to call out experts to come and help me.
_________________________

what's the situation that I can use call out?

Samuel

[Mister Micawber]

.
call out
a. to speak in a loud voice; shout. 'I called out to her from across the street.'
b. to summon into service or action: 'Call out the militia!'
c. to bring out; elicit: 'The emergency called out her hidden abilities.'
d. to direct attention to with a callout: 'to call out each detail in an illustration.'
e. Informal. to challenge to a fight: 'The sheriff called the outlaw out, and they both drew their pistols and fired.'
.
_________________
Canadian-American native speaker
who teaches English for a living at Mister Micawber's
ESL cafe: Interview with Mr. Micawber