I would keep the phone for now. I would also work with her to find a compromise that you can both live with. Maybe going through the old clothes slowly to weed them out and then working the new ones in. Maybe giving her a box or two for the old clothes so they can be stored somewhere and the new ones can be put away. Maybe hang up most of her clothing if that is possible given closet space. One of my cousins has a daughter who used to completely freak out over any new clothing. This started before the child was 2, so it wasn't a teen suddenly balking at a chore. She literally just couldn't cope with the idea of new clothing. Her mom would buy clothes a season or two ahead and then put them in her drawers for a couple of months before even trying to put them on her. Having seen them for some time, they were less upsetting to her. Getting rid of old clothing was a LOT harder. The girl would suddenly focus on some old shirt or pants and and completely lose it if they were not there. Even when the clothing literally wouldn't go on her, having the clothing taken away was a huge problem. After a couple of years of this, I suggested using the favorite old clothes to make a quilt. It just seemed to me like the old clothes were a security blanket of sorts and I suggested a "work in progress" type of quilt. The grandma of the little girl would cut the clothing into large squares and sewed them into another row on the quilt. Even the backing, when it was large enough for that, was put on piecemeal so the clothes didn't just disappear. They never even left the house or the girl's room unless it was to be washed or sewn on, and it helped her cope.
I think that you could work together with your granddaughter to figure out a solution that you both could live with. Maybe a t-shirt quilt from the favorite old shirts, or just storing them until she can cope with letting them go. Or some new storage arrangement for the current clothing. An incentive or reward for parting with old things (maybe take nice items to a consignment store so she can sell or trade them - the nicer care you take of your clothes, the more they give you for them, so it provides incentive to take care of them).
Does she have any idea of how much work goes into laundry? At age 12, my older brother took over the family laundry. It usually took an entire Saturday or Sunday. He did a very good job. Our mom was in grad school and we all had chores like that. I did all the dishes every day (I was 10.). Once you know how much work goes into the chore, you may be less likely to disrespect someone else's hard work. So maybe you could do the laundry together for a week or two, so she sees all the steps, and then she could take over her own laundry or all the laundry. Or at least she would see how much work it is, and if she disrespects you then (which seems to be part of the issue), you could tackle that side of the problem.
I think it is very good that you took the phone away. NOT because laundry was EVER that big of an issue for me as a mom, but because you followed through on the consequences. Kids NEED that, even if they don't want it. It is the least fun part of parenting, but one of the more important parts.