Any symmetric encryption is ~free compared to the cost of a network request or db query.

In this particular instance, Speck would be ideal since it supports a 96-bit block size https://en.wikipedia.org/wiki/Speck_(cipher)

Symmetric encryption is computationally ~free, but most of them are conceptually complex. The purpose of encryption here isn't security, it's obfuscation in the service of dissuading people from depending on something they shouldn't, so using the absolutely simplest thing that could possibly work is a positive.

XOR with fixed key is trivially figure-out-able, defeating the purpose. Speck is simple enough that a working implementation is included within the wikipedia article, and most LLMs can oneshot it.

A cryptographer may quibble and call that an encoding but I agree.

A cryptographer would say that XOR ciphers are a fundamental cryptography primitive, and e.g. the basic building blocks for one-time pads.

Yes, XOR is a real and fundamental primitive in cryptography, but a cryptographer may view the scheme you described as violating Kerckhoffs's second principle of "secrecy in key only" (sometimes phrased, "if you don't pass in a key, it is encoding and not encryption"). You could view your obscure phrase as a key, or you could view it as a constant in a proprietary, obscure algorithm (which would make it an encoding). There's room for interpretation there.

Note that this is not a one-time pad because we are using the same key material many times.

But this is somewhat pedantic on my part, it's a distinction without a difference in this specific case where we don't actually need secrecy. (In most other cases there would be an important difference.)