This claim that texting can cause arthritis is partly true. Arthritis is a chronic health condition where your body can cause pain or stiffness. A very common condition, affecting around 60 million Americans today, can possibly be connected to texting too much on your cellphone. A UCLA Health study explains that the average person with a phone texts around 5-6 hours every day. When texting, your thumbs move very often and quickly, which can lead to inflammation in the thumb joint and tendon. With this overused joint movement, experts are starting to see a connection between typing on your phone to an early diagnosis of arthritis, yet, "texting is still a relatively new activity and arthritis can take many decades to develop — so the full relationship remains to be seen," says UCLA Health. Another study by Yale Medicine backs up the first claim, talking about arthritis concerns with your thumb. Dr williams, an expert mentioned in this source, explains how they have not found enough evidence that executive phone use can directly cause arthritis. Being on your phone too much can aggravate existing issues. Thinking back to the claim after reading these studies, it’s clear that the claim is misleading and exaggerated. There is no direct correlation between excess phone use and arthritis, only a factor that could increase pain in a condition that has already been diagnosed.
Sources: 
https://www.uclahealth.org/news/article/can-texting-give-you-arthritis 
https://www.yalemedicine.org/news/is-there-a-link-between-hand-pain-and-your-smartphone-use