As you obviously use one for fitness purposes I wonder if you had considered completely replacing your iPhone with an Apple Watch for day-to-day uses. Bar photography it offers everything you need in terms of communication and apps but without any distracting games or social media. You could just turn on the 4G whenever you needed to see if you had any messages and then back off again to save battery.

Use your iPhone to download all the music and podcasts you need and then just put your iPhone in a drawer until the evening.

If you wanted a device to manage all the other work things but not be as distracting then any model of iPad would do the job but again, because its either sat on a desk all day or locked away in a backpack its not as big a distraction as that phone stuck in your pocket.

Photography? Buy yourself a nice Sony A6000 mirrorless camera. Its small and light enough to carry in your daily bag but much better than any phone at imaging)

(TBH I'd love it if Apple brought the Watch app to iPad OS and let us bypass the iPhone altogether)