they are owned by Marvel, Inc ( the comic guys )
Monolith
Do you have too many ideas and you don't know which one to write? Write that one you're most interested in, or combine two or three ideas you like the most and write a novel.
Do you have a story you're in the middle of that you don't like anymore? Stop writing. It's okay to abandon a work in progress. It's part of writing, for beginners, amatures, and professionals.
Do you have ideas that are trademarked and you don't want to get into a legal battle with Marvel Comics? Either don't write it, or contact Marvel Comics and see if you can sell it to them.
As long as working for Marvel is your ultimate goal, then you should initially stay away from any plotlines, characters, or even ideas that seem clearly derivative of Marvel's stuff (at least in your published work--if you have a private penchant for writing superhero stories, then that is all to the good). However, if working for Marvel is not your goal, then you can get as close as you want, as long as you don't actually violate trademark.
As long as any consumer can tell the difference between your characters etc. and Marvel's characters etc., then you're fine (but remember that consumers are the people that mistake Sunlight TM for Sunny Delight TM and sue both companies when they drink dish soap).
I'm not entirely sure what you mean by trademarked phrases. That could be interpreted to mean that you can't actually think of your own words for your characters to say or something. That would be a very bad sign indeed.