For GiveWP users, you can easliy add custom field and its data to the donation history CSV export.

add-custom-field-in-csv-givewp.php

<?php
/**
 * Add data to CSV column.
 *
 * @param array $columns List of CSV columns.
 *
 * @since 1.0.0
 *
 * @return array
 */
function custom_prefix_add_data_to_csv_column( $cols, $columns ) {
	$cols['phone'] = esc_html__( 'Phone', 'text-domain' );

	return $cols;
}

add_filter( 'give_export_donation_get_columns_name', 'custom_prefix_add_data_to_csv_column', 10, 2 );

/**
 * Add data to export CSV.
 *
 * @param array        $data     List of prepared CSV data.
 * @param Give_Payment $donation Donation Object.
 *
 * @since 1.0.0
 *
 * @return void
 */
function custom_prefix_add_data_to_export_csv( $data, $donation ) {
	if ( 'ipay88' === $donation->gateway ) { // Select the gateway slug for which you want to add the field.
    // Use the custom field meta name instead of `_mg_give_ipay88_phone` to fetch the correct value.
		$data['phone'] = ! empty( $donation->payment_meta['_mg_give_ipay88_phone'] ) ? $donation->payment_meta['_mg_give_ipay88_phone'] : '';
	}

	return $data;
}

add_filter( 'give_export_donation_data', 'custom_prefix_add_data_to_export_csv', 10, 2 );