When walking into a store, if you know what you want you absolutely welcome the sales assistants help right away.
When you want to browse, the persistent assistant is super annoying and you just want to leave.
No different on your website.
If you have a form that includes adding a phone number by force a call 5 minutes later is likely unwelcome.
Knowing when to let people browse, and when to assist makes for a great user experience rather than a frustrated one.
Slowdown cowboy, an interested buyer will put their hand up when ready.
Patience, generosity and volume are the keys.