Using Essential pckg. Busy with setting up a custom Invoice form. Stuck with two issues: 1) In 'Çontent' Can't change the phone number. 2) How to Add/del more columns?

Welcome to the Community forum, @drlornaeva. I'm here to lend a hand. 

In QuickBooks Online (QBO), you can change the phone number to be shown on the invoice by going through the Account and Settings page. 

Here's how:

1. Click the Gear icon at the top. 
2. Under Your Company, select Account and Settings.
3. Select the Company tab.
4. Go to the Contact info section, then click the pencil icon.
5. Enter the new number, then Save.
6. Select Done.

To add another field on the invoice, here's what you'll need to do:

1. Go to the Plus (+) icon and select Invoice.
2. Select your customer.
3. Click the small Gear icon on the upper right corner of the screen.
4. Under Fields, click the + Add another field link.

Moreover, I don’t want to leave you empty-handed, you'll want to visit our Community Help Articles hub in case you need some related articles in managing your account.

If you need anything else, leave a comment below. I’ll be here to help. Take care and enjoy your day!