When your child proves that they cannot handle the technology a smart phone provides responsibly, my recommendation is to simply take their phone. This will definitely be easier if you have set rules and expectations prior to taking it, but you know your child best. If they are engaging in risky behavior online, you need to take action and take the phone. Here's why:
Once a tween or teen starts taking risks online, whether it be vulgar comments, sexting, bullying, stalking, being on their phones in the middle of the night, whatever the case may be, they aren't going to suddenly wake up two weeks from now and stop. They are kids. They believe they are invincible, and it is difficult for them to think beyond the "RIGHT NOW". They won't stop until something happens that is either super hurtful or that gets them into trouble. As parents, we need to help them move beyond that, before it happens if possible.
I know it's not practical for them to be without a phone because of schedules after school and safety, etc., so I do recommend a replacement phone for however long and often is necessary, and here it is (notice the url - ha ha):
Here's what it will do:
* Give you both a break from the drama
* Give your child the opportunity to realize you are serious about your rules and their choices
* Give your child a chance to disengage from social media for a while
* Give you a chance after the dust settles to sit down together when neither of you are upset and create a set of rules around technology use that includes limits, content, and monitoring (I do recommend Bark).
It will take a few days for them to settle down, to not be so mad, but in most cases, as they decompress (because they don't have the tools to stay online), they will start to realize things were out of control. They may even feel relief from not "having" to be in constant contact with everyone immediately or to be forced out of a situation where they may have been in over their head.
SOME STATISTICS ABOUT TEENS AND ONLINE BEHAVIOR
Here are a few tidbits for you from the Pew Research Center. I hope you find it helpful.
Obviously, there are positive statistics about life online, but for the purpose of today's discussion we'll save those for another time.
You will not outsmart them with tech. There is always a loophole. But you can make them take a break, press reset and start over with a better plan in place. But not overnight. It takes time to detox from anything, phones and the online world included. I would not recommend giving them back the smartphone until they show over a period of time that they will honor what they have agreed to, and if they violate that agreement in any way, then back to the flip phone they go until they've absorbed the lesson and understand how things are going to be. Your biggest challenge will be consistency on your part.
If doing this doesn't help your situation, if you find they still aren't obeying the rules they agreed to (ie burner phones, new accounts, using Google docs, or web browsers, etc., etc.,) then it is likely time to seek additional resources to help you and your child get to the root of the problem. The symptoms of lying and hiding will likely not end until the underlying issues are addressed.