Step to insert PHP Page in Salesforce:
1. Go to setup->Create->Tabs in Salesforce:
2. Under Web Tab, click on new button. Now you can select the Page layout you want to set – full page width or 2 columns with Salesforce.com slider:
3. Fill the details type of tab, name of tab, height of the content frame in which tab data is showing. And Click next button:
4. Now save the url of your page in the Button or Link URL(Make sure your page is HTTPS with SSL). AS url with HTTP is not properly shown in the tab due to security issue:
5. Then after this, in Step 4. Add to Profiles click on Next.
6. In Step 5. Add to Custom Apps click on save.
7. Now you can go to the created tab. It’ll display PHP web page output, similar to this: