Check parent field is null before inserting child record

Hey,

As per my requirement,I need to check whether phone field of account object is null before inserting contact.If it is null,I should not allow user to create contact.I created trigger for this scenario,but unable to achieve functionality .I am posting my trigger code,any one please help me out?

Please help.

I didn't find the right solution from the Internet.

References:-

https://developer.salesforce.com/forums?id=9060G0000005UutQAE

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Thanks