Thanks so much for your email. I took today off to [rest/relax/travel/spend time with family]. In an effort to come back fully recharged, I won’t be spending today with my phone attached to my hand. (Scary, I know.) Don’t worry, though, because I will be checking in every so often and responding to anything urgent.
My phone just sits there gathering dust, so the only OOO message I need is the one I put in my email. Something like “I’ll read my email again on X. If you need assistance before then, please contact my colleague NN.”

I used to work with someone who had a message telling people she only checked her email twice a day. You pretty much needed to call her if you needed anything outside of those times. (She worked in a remote office.) I think she had read one of those books on efficiency that recommended scheduled email time. But there were problems with this: 4. My department often had to email attachments or text to illustrate our questions/concerns. And we were on deadlines. Reading a page of text over the phone was not an efficient use of anyone’s time 5. She did outreach & was often out of the office on site visits, trainings, or travel to these places, but never ever set her OOO for these, because she was “working.” However, she was effectively not available to read emails from other staff until after hours on those days.
To customize “Respond with Text“ for incoming calls, go ahead to iPhone Settings > Phone > Respond with Text > Edit “Respond with Text” messages.