Whenever I get phishing SMS they always come from a random 10-digit phone number so it's pretty clear they're scams. Reputable companies send these types of messages with short-codes, which are a 5 or 6-digit numbers that is very expensive and require thorough vetting by the carriers.
Don't get me wrong, carriers have been making strides to lower the amount of spam that's sent through the air (A2P requirements, toll-free number verification requirements, etc), but a determined scammer can still exploit SMS/MMS pretty easily.
Most people will trust a toll-free number just as much as a shortcode, and since tons of legitimate companies use toll-free numbers for messaging it just blurs the line of what a "reputable" number looks like.
Even SendGrid, which is owned by Twilio, uses toll-free numbers for their 2FA messages instead of shortcodes.
As far as I could tell (although I retired in 2019, so might be out of date), you can't use one short code through multiple aggregators, so if you want the benefits of multiple routes, you've got to have multiple shortcodes or live with sending from regular phone numbers.
Sadly, Novant Health (a hospital system) uses a regular 10-digit number for their patient portal 2FA. When I was in college, accessing sensitive info like your SSN and W2s in Banner also had 2FA via a 10-digit number. (This was an entirely separate system from the login 2FA provider, Duo, which uses shortcodes in addition to U2F tokens and their app.)