I'm a fairly direct person, but if I were concerned about injuring someone's feelings, I'd tell them, "I'm not crazy about texting, so please forgive me if I'm not keeping up with yours." If they continue to text you, just ignore most of them and reply to those you sincerely wish to reply to. Eventually they'll either understand, or they'll decide to take offense anyhow -- and that's not your issue, it's theirs.
I happen to dislike phones, and am constantly aggravated by needier acquaintances who depend on constant phone contact. I'm pretty candid with them: "I'm not a phone person. That probably won't change." I look at phones and computers as MY tools; I'm not their tool, and I elect when I do and don't use them.