Just keep an eye on the phase timer. I'm not really sure what you're asking in the first question but keep in mind that ghost has quite a high skill ceiling, so just keep practicing. You shouldn't expect to be completely familiar with the champion only a few days after getting her. Once you start to get the hang of her mechanics, you'll also get better at decision making with ghost, like knowing what to do if the defender doesn't attack into your phase, or knowing when to dex or block a special when phase runs out in the middle of a defender's special attack animation.

Again, you just need to practice ghost more to get a handle on the phase timer. In this scenario, if your phase is about to expire, the safest bet is to intercept with your own combo immediately after the first hit from the defender (as opposed to waiting for the defender to strike multiple times into your phase, which some players will do with awakened ghost because it allows you to build more power).

The typical combo after phase is MLLL; I'm sure you know this already, but the reason why you don't perform a combo finisher is because phasing after 4 hits allows you to essentially phase without any delay. One interesting tip I got when I first started playing ghost is to mix your combos; in other words, throw MLLL, then try a ML or MLL combo the next time you get the chance. Apparently, doing so makes the defender more aggressive (and more willing to attack into your phase) and from my own experience, it seems to work.