teenage mobile phone usage and procrastination

My daughter is a senior in high school, already ready to graduate. We did not get her a phone until this year, but she still seems to lack the ability to control it. For example, when she gets home from school, she would lie on the sofa and scroll through her phone. Sometimes, she would also take a long nap. She does not start her homework until 8 or 9 pm, sometimes even later. And then she stays up late into the night to finish it. The next morning, she would get up late and be late to school. This is almost a daily occurrence. With such bad habits, I am concerned that she would struggle in college, where there is even less structure. She's 18. But she does not act like an adult. I am thinking of getting more control over her phone, like setting up screen time limits. But I know that whatever I do, it will be a fight. She only have 3 months of staying at home, and we don't want to ruin our relationship with her before she goes off to college either. What's your suggestion?