If you're having problems with phpize not found on CentOS7.x after you have installed the relevant devel tools for your version/s of PHP, this path finally worked for me:
For PHP 7.2.x
/opt/cpanel/ea-php72/root/usr/bin/phpize
For PHP 7.3.x
/opt/cpanel/ea-php73/root/usr/bin/phpize
For PHP 7.4.x
/opt/cpanel/ea-php74/root/usr/bin/phpize
Run this in your folder containing the downloaded PHP extension, for example in line 3 below:
git clone --recursive --depth=1 https://github.com/kjdev/php-ext-brotli.git
cd /php-ext-brotli
/opt/cpanel/ea-php73/root/usr/bin/phpize
./configure --with-php-config=/opt/cpanel/ea-php73/root/usr/bin/php-config
make
make test