To change the mobile view for full-width layout into the stacking of the date, image and content please add the following CSS in Divi Theme Option.

@media screen and (max-width: 767px) {
    .et_pb_post_extra.el_dbe_full_width {
        padding: 30px 0;
    }
    .et_pb_post_extra.el_dbe_full_width .post-date {
        margin-bottom: 20px;
        padding-right: 10px;
    }
    .et_pb_post_extra.el_dbe_full_width .post-media {
        width: 100%;
        margin-right: 0;
    }
    .et_pb_post_extra.el_dbe_full_width .post-content {
        width: 100%;
        margin-left: 0;
    }
    .el_dbe_full_width.et_pb_no_thumb .post-content {
        width: 100%;
        padding: 0;
        margin-left: 0;
    }
}