It depends on the ease of different individuals to decide whether to keep it in shirt's pocket or the one in trousers. Regarding health hazards, there have been numerous studies where it has been suggested that long term carrying of phone near the heart may cause health issues, specially when the signals are weak. Similarly, there have been claims were researchers suggested carrying mobiles in our trouser pockets may affect our reproductive system. However, we cannot deny the requirement of carrying a mobile with us all the time. Therefore, I would like to provide my opinion further...
So far, I have carried phones and smart phones of different sizes, all in my trouser's pocket. Mostly in the left pocket of my jeans or pant. In this case, I am quite opposite from what suggests. I think my smartphone or anything that I put in my shirt's pocket remains more prone to be lost. At least that is what happens with me, therefore, I have never carried anything there except identity cards.
I am pretty much used to carry and feel its presence in my trouser's pocket all the time.
Mostly, I don't even carry a wallet unless necessary, and like to keep the cash as it is in one of my pockets. To ensure that I don't drop them somewhere, I keep them in another pocket of my trouser. Basically, left pocket is mostly and fully dedicated to smartphone.
(I found it quite funny to read where author asks about carrying phone in the hip pocket. All we will need is a little forgetfulness to damage our phones by our weight, as we sit. I guess, hip pocket is only better to carry extra handkerchiefs. Even carrying a wallet in hip pocket may make it prone to thieves and otherwise causing discomfort while we sit, and then disturbing the original, ideal shape of our wallets.
"Your value does not decrease based on someone's inability to see your worth"