Example #1 Mark: Ugh! I can't believe we have two more weeks of working twelve hour shifts left to do. I don't know if I can do this much longer. Stacy: Yeah. I know. It sucks but if we can just tough it out, we will be getting a lot of money for this job. Mark: True. I just need to man up to the task. Stacy: Hahaha. Yeah, you do. Example #2 Mark: I can't stand how rude my sensei has been lately. I leave class thinking that I am never going to be any good at Aikido. I swear I feel like quitting! Stacy: Don't be so hard on yourself. She is just being harder on you guys lately because your test is coming up next month. If you tough it out and practice every day, you will get your black belt next month and then class and her attitude will return to what it was before. I promise. Mark: Well I will try but I hope you're right. Stacy: I am. You'll see.

It's actually more of a set expression than a phrasal verb. We don't replace "it" with anything else. However, the verb can still conjugate. This phrase just means you accept the situation (usually something that requires effort or patience from you) and do your best. "I knew it would warm up, so I was going to tough it out. On the second day of the chilly temperature, I broke down and turned the furnace on." (about tolerating cold weather) "We do NOT recommend toughing it out with a home remedy..." (about dealing with an illness) "Hawthorn were hardened because they toughed it out against Port Adelaide." (about a rugby team's recent match)