If my client saves my contact details in his phone and I change my phone number, will the new number be reflected in his phone?

No. Once your client saves your contact on his phone, your contact data is copied from your QR Code business card or vCard QR Code on his phone. The contact data is not linked or synced with your client's phone and therefore cannot be updated remotely.

If your contact data changes, for example you have a new number, the best way is to send the updated vCard to your clients in an e-mail. If you have QR Code Business Card you can simply click on Options and then vCard to download the updated contact.

Now you can send the downloaded vCard as an attachment in an e-mail or you can also send a direct link by right clicking on the vCard link shown below and copy the target URL.