There's a more nuanced answer than just no phone at night, speaking as a secondary safeguarding lead.
What is your relationship like with your daughter @Annimoore? Because that attachment bond is key here.
Yes, you need to start establishing limits and monitoring of phone use with teens, but getting this to happen without a fight is the first step, then working on doing it without resentment and bitterness is important - because if you don't work on that, you'll just end up encouraging secrecy from your teen.
What you want is openness. The gold standard is a teen who can self-regulate their online persona.
How do you teach a teen to use a critical mind and recognise when online content might be harmful - faked, doom scrolling, echo-chamber, and so on? That starts with connection with your child. Talk about what they do online non-judgementally, all the time. Aim to be interested in what they are doing, rather than judgemental of it.
In terms of screen time - again, it comes down to being able to talk to your teen on their level, rather than talking down and dictating. It's OK for teenagers to sleep in if they don't need to be up in the morning, but what about when they do? Your 15yo will be able to work out that they'll feel rubbish going to sleep at 3am if they have to be up at 7am. So how could you help them to feel less rubbish? The regulation can come from the teen, it just ususlly needs some parental prodding and guiding to get there.
However, that all comes with recognising that - if teen has no reason to be up the next day, what harm is phone use doing? You need to be ready to answer that because "because its unhealthy" or "because I say so" will get you no where. Would you have no issue with 4h of daytime phone use but big issues with 4h of nighttime phone use, with no other rationale than time? Because that's illogical and a "because I say so" answer. You need to go further underneath and that may create questions about your own general parenting.