Phone cameras are extraordinary and getting better. It would be dishonest for a studio to pretend otherwise, so here is an honest account of where they are enough.
Where a phone is genuinely fine
Everyday documentation. The daily record of a child growing up is better captured by the camera you have in your pocket than by four studio sessions a year, and it always will be.
Good light, close subject, no complicated background — a phone handles that beautifully. Most family photographs fall into this category and do not need anyone else involved.
Where it stops being enough
When you need to be in the picture. This is the big one. Most families have no good photograph with everybody in it, because someone is always holding the camera. That is not a technical limitation you can solve with a better phone.
Difficult light. A ceremony in a dim hall, a candlelit festive frame, a backlit outdoor portrait at the wrong hour. Phones apply heavy computational processing to survive these, and it shows — waxy skin, crushed shadows, halos around edges.
When the moment cannot be repeated. A newborn's first fortnight, a wedding, a grandparent who is here now. There is no second attempt, and that is where redundancy, experience and someone whose only job is watching the room actually matter.
The thing that is not about the camera
Most of what a studio session provides is not resolution. It is a built set, controlled light, someone directing so nobody has to work out what to do with their hands, a handler keeping a baby settled, and an editorial pass afterwards.
You could not replicate that with a better sensor.
An honest recommendation
Keep taking phone photographs constantly. Book a session for the things that cannot be redone, and for the frames you need to be standing in. That is a smaller number of sessions than most studios would like to sell you.