Part of being a grownup is doing whatever the hell you want. If you don't want to pick up that phone (and have a potentially awkward conversation with some sleazebag recruiter that's trying to sell you on a shit job you don't want), don't.
This reminds me of the people that think women (or men) that don't want to go out with them owe them some kind of explanation. No, dude. Get some social awareness and move the fuck on.
Sure, you can do whatever you want. That doesn't change the fact that people will consider u a prick and a coward if you ignore calls for weeks on end without any explanation.
It's not the same thing. You can skip a call out of the blue, but after you have had some kind of interaction, is really good manners to have open and direct discussion. Both professionally and in the example you mention.
Part of being a grownup is doing whatever the hell you want. If you want to ring that phone (and have a potentially awkward conversation with some immature developer that's not yet picking up on your opportunity), do it.
The rights come with responsibilities and/or consequences.
Being an adult means you get to own many of your choices, but also their consequences.
Giving the recruiter a direct "no" would be far more professional. OTOH, I've dissed more than my share of recruiters myself, though generally only after an initial clear and unambiguous communication wasn't respected.
This reminds me of the people that think women (or men) that don't want to go out with them owe them some kind of explanation. No, dude. Get some social awareness and move the fuck on.