To access opportunities data from Salesforce via soap api call get security token, Username and Password.
Also need force Soapclient library files. You can get these files from this link https://github.com/developerforce/Force.com-Toolkit-for-PHP/tree/master/soapclient
You can get opportunities data through query string for example Select Name, Opportunity_ID__c From Opportunity. Select required parameter data as per you need.
Use below sample code to execute the salesforce api in php: