What's the meaning of ¡Yo más guapa! in the following conversation?
A: - ¡Toma, te quiero!
B: - ¡Yo más guapa!
I googled the phrase and it seems to be some kind of slogan. I'm not sure though whether it is somehow connected to what is meant here.
You are missing a comma there. The phrase should be: yo más, guapa.
guapa means good looking and it's a common way to affectionately address a woman in Spain. So the conversation goes more or less like this:
A: - ¡I love you!
B: - ¡I love you more, gorgeous!
I think it may need a comma
¡Yo más guapa! Me more, cuttie
It is not an slogan, but a colloquial way of telling someone that you want or deserve or need something more than the other person.
A:- No llego a fin de mes. Necesito otros 500 euros
B:- Yo también, guapa
In that context guapa
is not a colloquial way to refer to somebody, but means literally "beautiful".
A:- ¡Te quiero!
B: - ¡Yo (a tí) más, guapa!