I am adding an answer based on my experience and also thanks to Michael Cropper and Salman von Abbas for their inputs.
The php.ini file is created when php is installed on the server. I believe that wordpress installation requires php to be installed on the server. So your webhost typically installs it on their server and then sells you the hosting space. Then you install your wordpress on it.
Hence, it follows clearly from this that the php.ini file will not be present in the wp-admin folder.
So you need to look for it either at your root folder (but most likely it won't be there if you're on a shared webhosting plan). Then you need to create a file as such:
create a new file in the location = /public_html/your_domain/any_name.php
Put the following code inside the file:
<?php
$inipath = php_ini_loaded_file();
if ($inipath) {
echo 'Loaded php.ini: ' . $inipath;
} else {
echo 'A php.ini file is not loaded';
}
Now try to access the file through your browser as follows:
https://your_domain/any_name.php
This should show a message that clearly states the location of your php.ini file.
If you're on a shared hosting plan then you probably won't have access to this folder. You will need to inform the web hosting support to take care of this for you.
Hope this helps!