More and more developing countries are beginning to implement a system, in which a worker can decide for himself how to work.
I'd delete the comma.
if a person has a family to look after and he cannot work the whole day he may work freelance
I'd put a comma after 'day'
This term has come under fire- you could use developing countries, which is the PC term.
the salary is comparatively high for such a job
I'd delete 'for such a job'
have to meet a deadline
I'd put a comma after this
-Should anybody phone me, tell them/him/her I'm busy. I'm really confused.
I'd use 'them'. When a person's gender is unclear, I always use the plural, even with things like 'somebody' that are singular.