How to stop my 3 year old bad behaviour

My son has recently got into some really bad habits.

When I'm on the phone he shouts for me to shush or screams at me for attention so I tell him to shut up or mute myself and tell him off and to be quiet because it's rude to deliberately scream and stomp his feet cause I'm always ALWAYS giving him attention.

He doesn't understand the concept of the word Jo and sometimes if he's about to do something naughty he never buys it when I say santa is watching or his auntie won't be happy etc.

I'm a single mum so I'm having to be both the good and the bad cop here. I never come across as being intimidating if I shout, I do take him in time outs on the naughty step also and I always always get him to apologise for any bad behaviour he's done.

What can I do to help stop it or do I carry on with what I'm doing and ride it out till he grows out of this phase???