You can do the entire mission without a mic. There's ample time to use text chat for all the mechanics, but many players think the last one moves too quickly to be done via text chat.

But actually...

The clock only shows THREE combinations, looped over and over again. Both players just need to type down what they see in each of the three combinations. Don't shoot anything yet.

Then once all combinations are written down, tally them up and identify the common one in each combination.

Then shoot.

If you get any wrong, the combinations will change. So just watch the 3 new combinations again and type them down.

Example of text chat:

[PlayerA]: 2 3 7 8

[PlayerB]: 1 4 7 11

[PlayerA]: ---

[PlayerA]: 1 3 6 9

[PlayerB]: 6 8 10 11

[PlayerA]: ---

[PlayerA]: 5 6 7 10

[PlayerB]: 4 5 11 12

[PlayerA]: ---

[PlayerA]: 7 6 5

[PlayerA]: Start the next round after I emote

Is it complicated? Yes it can be messy. But it's not impossible. Don't be pressured into voice comms if you struggle with it. Find like-minded guardians and do it with them.

To have enough time to do this, put on a machine gun and focus fire on the bosses, don't waste too much time on adds. Do the prior mechanics quickly -- find the symbols, run to a safe corner and type them out.

EDIT FOR AN EVEN CLEANER WAY OF COMMUNICATING:

The 3 combinations are also on a KNOCKOUT. This means that once you correctly shoot 1, the loop will only contain the remaining 2 combinations. Once you correctly shoot the next combination, the remaining 1 will keep appearing.

This means you don't have to follow my above method of typing all 3 and syncing all 3. You can do it one by one. In fact, this is easier as some trash adds spawn in between, so it gives you some time to clear them before moving on to the next set.

Example of text chat:

[PlayerA]: this one, now.

[PlayerA]: 2 3 7 8

[PlayerB]: 1 4 7 11

[PlayerA]: one more time to confirm that we're looking at the same one.

[PlayerA]: 2 3 7 8

[PlayerB]: 1 4 7 11

[PlayerA]: great. the next time this combo comes around, shoot 7.