While you might think a “burner phone” is something only a criminal may use to avoid being tracked by authorities, law-abiding citizens may also appreciate the privacy awarded by a burner phone.
The details may be found in a article by Marc Saltzman in the USA Today web site at: https://tinyurl.com/privacy190912.
Here is another idea: An even more secure and private “telephone” can be fashioned from an Apple iPod touch. Details may be found by starting in this blog at The Most Secure Way to Communicate? An iPod Touch at https://privacyblog.com/2015/08/20/the-most-secure-way-to-communicate-an-ipod-touch/ which then refers the reader to The Most Secure Way to Communicate? An iPod Touch at https://www.wired.com/2015/08/secure-way-communicate-ipod-touch/.
After reading that last article 4 years ago, I purchased an Apple iPod touch and use it occasionally as a privacy-enhanced substitute for a cell phone.