Should I get a business phone number?

I've thought about this same thing. I have a dual sim phone and might get a second number with US Mobile. It's $5/mo for 2500 minutes/ texts so not bad at all.

In the past I've used my personal number for business and it can get annoying if you change businesses because people will still call/text for the original business. I'm not sure if getting flagged as spam is as much of a concern unless you're doing tons of cold calls/texts.

+1 for Google Voice. One caveat though: some verification services will flag my GV number as not being a real number. In such cases, I had to enter my personal number.
+1 for US Mobile: my entire family uses it, it runs on the Verizon or T-Mobile network depending on the device and your preference. The UI (web and mobile) to manage subscriptions is great, so is their onboarding. They also have a generous referral program, so ask me for a referral code if you are going to use them :-D

I can also second the Google Voice option.

I've used it in the past and will continue in the future when I need a business phone number.

Google Voice is a great fit for this - I use it for business, classified ads, services where I'm unsure of how (if) the data will be protected. With the app installed on your phone you can use it just like any other phone app. It handles voicemail and texts, too, so it functions just like a "real" number, with an additional layer of protection.