Reply To: How do I make the text in the slides photos bigger only on mobile?

Add this to Customize > Additional CSS (change the font-size values to the size you want)

@media (max-width: 768px) {
    .hero-content-wrap {
        font-size: 16px !important;
    }
    .hero-widget-title {
        font-size: 48px !important;
    }
}