This example shows how to group several filters in the Members Directory of the Ultimate Member.

um_grouped_filtes.php

<?php

/**
 * This example shows how to group several filters in the Members Directory of the Ultimate Member. 
 * For example there are three phone fields in the profile ("Phone", "Phone number", "Mobile Number"), 
 * but you want to use a single filter "Phone number" to filter by these three fields in the Member Directory.
 *
 * Note: This example works if the setting "Enable custom table for usermeta" is turned off. 
 * See the gist https://gist.github.com/denisbaranov/dd8e7c0845af35eeba2bdd08f5f72a76 otherwise.
 * 
 * Change the variable $um_grouped_filtes. Add custom code to the file functions.php in the active theme directory.
 * 
 * Ultimate Member documentation: https://docs.ultimatemember.com
 */

add_filter( 'um_prepare_user_query_args', function ( $query_args, $directory_data_settings ) {
	global $um_grouped_filtes;

	// Add your grouped filters here in a format 'main_filter' => [ 'additional_filter' ]
	$um_grouped_filtes = apply_filters( 'um_directory_grouped_filtes', array(
		'country'      => array( 'billing_country', 'shipping_country' ),
		'phone_number' => array( 'mobile_number', 'phone' )
	) );

	if ( !function_exists( 'um_directory_meta_query__grouped_filtes' ) ) {
		function um_directory_meta_query__grouped_filtes( $filter ) {
			global $um_grouped_filtes;
			if ( is_array( $filter ) && isset( $filter['key'] ) && isset( $um_grouped_filtes[$filter['key']] ) ) {
				$grouped_meta_query = array(
					'relation'         => 'OR',
					"{$filter['key']}" => $filter
				);
				foreach ( $um_grouped_filtes[$filter['key']] as $metakey ) {
					$grouped_meta_query[$metakey] = array_merge( $filter, array( 'key' => $metakey ) );
				}
				$filter = $grouped_meta_query;
			} elseif ( is_array( $filter ) && !isset( $filter['key'] ) ) {
				$filter = array_map( 'um_directory_meta_query__grouped_filtes', $filter );
			}
			return $filter;
		}
	}

	if ( isset( $query_args['meta_query'] ) && is_array( $query_args['meta_query'] ) ) {
		$query_args['meta_query'] = array_map( 'um_directory_meta_query__grouped_filtes', $query_args['meta_query'] );
	}

	return $query_args;
}, 20, 2 );

This gist is a part of the article Use a single control to filter by several fields in the members directory

Note: This solution is not recommended because it significantly slows down the directory. The relationship between the number of combined fields and slowdown is power-law: combining two fields slows down the search by two times, combining three fields - four times, four fields - eight times, and so on. It's better to use a general search line that searches by all fields.