Whom do you trust your identity with more? Twitter or the regime you're under?
As much as I despise Twitter, I'd much rather that they exclusively know my identity than both they and the regime. This isn't to say that I agree with Twitter requiring phone numbers.
Twitter is not a "leftist organization". Contrary to the belief of the somewhat unhinged, there's no conservative-hating conspiracy of tech giants, which are on the whole not particularly left-leaning where it counts. There are absolutely conservatives on Twitter; there have always been and it remains that way now.
Twitter literally banned the sitting President of the United States, a Republican. Other Republicans like Marjorie Taylor Greene have had their accounts banned, while this has never happened to a Democrat. People were banned for questioning COVID (e.g. the lab leak hypothesis), banned for questioning the 2020 Presidential election's integrity (yet nobody was banned for speculating on Russian interference and calling Trump illegitimate in 2016), banned for misgendering or deadnaming transgenders. Conveniently all the wrongthink that fall squarely in opposition to progressive ideology.
I don't think anyone believes there's a secret conspiracy, it's more that the type of people who work in programming, and particularly for a Bay Area company like Twitter, tend to be very progressive. It's the same miasma that clouds the mainstream media, academia, and now most corporate PR.
As much as I despise Twitter, I'd much rather that they exclusively know my identity than both they and the regime. This isn't to say that I agree with Twitter requiring phone numbers.