Hi i missed the minyan for musaf today, and instead I thought to go as the shliach tzibbur to daven my shmonei esrei out loud (the whole thing.
Is there an idea to do that? Is it considered tefillah btzibur?
There is such an idea to do this, however it is not recommended, and it should only be done in a instances that you don’t have any other choice. The reason for this is that the order of davening is to say the silent shemona esrei first and only after that to say chazoras hashatz.
Regarding teffilah btzibbur – There are opinions whether it would be considered tefilah btzibur. According to some poskim, since you didn’t start together with the tzibbur it isn’t considered b’tzibur, however others say that even if one davens during chazora hashatz it is still considered teffilah btzibbur. Davening together with the shatz would be just as good in regard to teffilah b’tzibur, therefore I would recommend that you not daven as the shaliach tzibbur, but start shemona esrei together with the chazzan and say the shemona esrei together with him.
O:CH 122-2, M:B 4,6. Orchos Rabeinu 1 -162, See Eishei Yisrael 12-9 for the different opinions.