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.)