As others have aptly said, your iPhone model/age puts it beyond new OS support. And I believe your model is also outside the window of receiving security patches (though I’m not 100% certain). IPhones beyond OS support but still receive security updates can continue to be used. Whether apps/features continue to work will be on a case by case basis though compatibility will get worse as months go on. However, if your iPhone is also beyond seeing security patch versions, I urge you to get a new iPhone. Once security vulnerabilities are no longer patched, it is imho too much of a security risk to be connecting the iphone to the internet.