Even if you need to get a new smartphone besides the way of paying for it (and bitcoin can help to bypass sanctions this way) you need a way of getting it. And if it is prohibited to send it into Russia then first step with paying for it will not work anyway. So bypassing sanctions is a complex problem. Goverments which implement sanctions can work on not to let to import prohibited goods.
If you want to buy something from the country which is not supporting sanctions you can use or some of currencies of countries which are not supporting sanctions also, you can use gold, you can use barter etc. China is a neighbor country and there is no need to bypass sanctions with bitcoin, there are many more options.
So if someone wants to get some new gadget for his own it is not a real problem for the goverments which implement sanctions. And if there is a large volume merchandise imports they can prevent it from the areas they control and can't for the countries which are not supporting sanctions.
I would also believe that there are nations with no sanctions to Russia that can get the phones, or any other item. It could literally become like a business. X nation that has no sanctions from or to any nation, could get anything from any nation that Russians want, then sell it to Russians and Russians could use that. Which is a great way to circumvent all of this sanction stuff to be fair, even gas and oil could be dealt the same way, would make that nation a lot richer.
I would have to guess that west would have a problem with that and could create some problems and tensions, but what are they going to do? Sanction another nation? It doesn't work as well as they imagined from what we have seen.