There was so much that could be said in two simple words. Still, she and Cosima knew one another so well that it was obvious what those words meant even if they were short. Especially with Cosima who did talk a lot usually as it was just who she was. Just as she was the hands on type. So it had felt important to let her know in just the 'thank you' that she had helped more than she might realize.
"I'll see you soon."
With that, Jemma hung up and then hugged Bucky in thanks (and a bit to ground herself - if she could hug Melinda May, she could hug the Winter Soldier thank you very much) and it was back to the Agency. There was still a crisis going on, after all.