It doesn't matter if you're on your phone. Even if you train with 100% focus and clarity of intent, it doesn't matter if you're texting during your rest periods. They're rest periods. When you're on your phone you don't need to be thinking about weightlifting and when you're lifting, you don't need to be thinking about your phone.
Distractions are distractions, and we will always need to focus our attention on a thing if we wish to become skilled. And that's the thing about "being on your phone". It's not about the phone. It's about your training, and giving yourself an opportunity to have a real experience of the thing you're doing. Whether you play with a phone or not is irrelevant. There are hundreds of ways to train, some are serious and some are casual. It's not up to anyone else. If you want to apply effort, you'll apply effort and if you want a casual, relaxed workout you can have one of them too.
And your rest periods, if you have any, they belong to you too. Your phone doesn't complain if you're thinking about training while you're playing with it, and the weights don't care if you're distracted or not. In the end it's all for you. Some workouts are going to be focused and targeted, and sometimes it's just fun to mess around. If you're going to train, experience it all.
I doubt it's my best blog post, but I wrote it during rest periods. Yay for efficiency!