Op Try and get hold of the book 'Untangled' by Lisa Damour. It was recommended to me on here and is very good on raising teenage girls.
You are not a crap mother or a failure.
Your daughter is beginning the normal adolescent process of cutting herself off from you and your dh. That doesn't mean that you have to tolerate door slamming and rudeness of course, but it means that you can give yourself a break, step back a bit, and try and not take her behaviour so personally.
Keep calm in the eye of the storm and tell your DH that you need his support to back you up. ( Prepare him in advance about this and not just when it is all kicking off. Have a code word or a special 'look' if he is clueless. )
Don't be a pushover, and don't give up on encouraging her to be up and out on time , for example, but keep it all very factual and calm, no shouting or personal criticisms, just calmly state the facts such as "it is 7.30 am and breakfast is ready" or whatever even though her behaviour is driving you crazy inside!
Tell her that you love her a lot (teens need to hear this often) and that you love her but not her behaviour sometimes. Tell her that you will always be available if she needs to talk, but from now on she needs to start taking a bit more responsibility for her own actions. Tell her that she can earn some freedom that way , as freedom is built on trust and following through once you have agreed to do something.
At the same time, do the one-on-one stuff that is enjoyable. That way you don't get in to the negative cycle of all of your interactions being snippy.
It's fine imho to have a phone at 12 for safety reasons. Mine wasn't allowed to keep hers overnight at that age though. And if her phone is your "currency" then use it. Ultimately though, your main disciplinary tool, is your relationship. It's your closeness and love for one another that will stop her going off the rails more than anything else, so keep building on that.
I am four years on from you and things are improving a bit so hang in there. It's a very difficult balance. My mother was far too strict and forgot to foster the feeling that she and I were on the same team. On the other hand, as parents, I do think we need to tweak the discipline a bit if a child is being horribly disrespectful, not least because they will be unhappy if there are constant meltdowns at home, even if they have caused them!
Good luck op. It's a tough road. Hang in there. 
Oh and don't worry too much about the hygiene thing as long as the grunge isn't extreme. My DD suddenly transformed from being a soap dodger to a shower hogger, the summer she turned 14! 
Finally, finally, another good tip I read on here, is to go out and do something for yourself. Take up a new hobby or interest. Something that makes you independently happy. That way, you will cope with the harsh words with more equilibrium, your emotional well-being won't be so tied to her ups and downs, and you will be modelling to her how to keep happy during a challenging time.