Captain phasma still good without the leader spot?

I don't think it is good if it is not leader.

And keep sid as leader or replace with phasma?

Between Sid and Phasma, Sid is better at leader only in comps with high crit attackers like FOTP, 88, Luke, 86, etc.

Phasma is better as leader when you have anything else, especially FO toons like Kylo, FOO, or even FOTP there because of the double assist rate.
I run a Phasma led team with Kylo plus Sid, Lumi and Daka. The extra stuns I get from Daka doing assists is really helpful. The turn meter manipulation is also a bonus that can give you an edge.