I have come across many girls, in first meeting some agree to give out their phone numbers why some say NO.
My question is, does rejecting a guy phone number request a sign of not wanting the guy or what?
Please men what are your experience, ladies what is/are your reason(s)?

Many factors could lead to a lady not given out her phone number or any contact information in first meeting, such as the type of lady you met and the mood of the lady.
Some see given out a guy a phone number as a being desperate or being cheap.

A lady given out phone number in first meeting has downside. As this could lead to abuse, so it requires time, at least to be a bit familiar with you, knowing the type of person you are before given out such.

Presentation and your approach determines if a lady will say Yes or No.
Another thing is how attractive are you? because is rare to see a lady these days with out at least one guy she is moving with or dating, so as you are communicating to  her her mind goes into many comparisons. This is bedrock whether to give you her phone number or not. So be attractive and appear valuable as much as you can to her to stand a chance.

Girls/Ladies tend to make life difficult for themselves, Imagine and handsome man with a lot of money to spend that want settle down and some ladies are here creating dullness to guy's intention?

Well, be patient with girls and follow them gradually and eventually you will get what you want from them.