How to compensate signal phase using tag stream in GNU Radio

Question

I am developing pulse radar using the BladeRF as the hardware and GNU Radio as the software. On my receiver part, I would like to do pulse averaging to increase the SNR. Therefore, I have to compensate the phase of the received pulses to its phase reference which is usually coming from the first pulse, then average them. For example, the 1sr pulse phase is 0 Rad then the 2nd pulse phase is 1 Rad. Before I added the 1st and the 2nd pulse, I will compensate the 2nd pulse, firstly. Once it is done, then I add the 1st and the 2nd pulse. I found a similar problem in this forum (How to save a changing variable in GNU Radio?). One of the answers said to use tag stream and he gives a brief explanation. Unfortunately, I do not understand and I am looking for any example code for the similar case but I could not find it. Can some one help me to find the solution? Thank you