I'd say this is what you are immediately looking for:
RewriteEngine On
RewriteRule ^/?page1/(.*)$ /page1.php?$1 [END]
RewriteRule ^/?page2/(.*)$ /page2.php?$1 [END]
But it might be worth to check if this cannot be generalized for arbitrary "pages":
RewriteEngine On
RewriteCond %{REQUEST_URI} !-f
RewriteCond %{REQUEST_URI}.php -f
RewriteRule ^/?(.+)/(.*)$ /$1.php?$2 [END]
In case you receive an internal server error (http status 500) using the rule above then chances are that you operate a very old version of the apache http server. You will see a definite hint to an unsupported [END] flag in your http servers error log file in that case. You can either try to upgrade or use the older [L] flag, it probably will work the same in this situation, though that depends a bit on your setup.
This rule will work likewise in the http servers host configuration or inside a dynamic configuration file (".htaccess" file). Obviously the rewriting module needs to be loaded inside the http server and enabled in the http host. In case you use a dynamic configuration file you need to take care that it's interpretation is enabled at all in the host configuration and that it is located in the host's DOCUMENT_ROOT folder.
And a general remark: you should always prefer to place such rules in the http servers host configuration instead of using dynamic configuration files (".htaccess"). Those dynamic configuration files add complexity, are often a cause of unexpected behavior, hard to debug and they really slow down the http server. They are only provided as a last option for situations where you do not have access to the real http servers host configuration (read: really cheap service providers) or for applications insisting on writing their own rules (which is an obvious security nightmare).