From the FAQ, a list of supported countries for Firebase Phone Auth:
Firebase Authentication supports checking phone numbers worldwide, but not all networks reliably deliver our messages for verification. The following countries have good shipping rates and are expected to work well for entering a phone number.
AD Andorra AE United Arab Emirates AF Afghanistan AG Antigua and Barbuda AL Albania AM Armenia AO Angola AR Argentina AS American Samoa AT Austria AU Australia AW Aruba BA Bosnia and Herzegovina BB Barbados BD Bangladesh BE Belgium BF Burkina Faso BG Bulgaria BJ Benin BM Bermuda BN Brunei Darussalam BO Bolivia BR Brazil BS Bahamas BT Bhutan BW Botswana BY Belarus BZ Belize CA Canada CD Congo, (Kinshasa) CF Central African Republic CG Congo (Brazzaville) CH Switzerland CI Côte d'Ivoire CK Cook Islands CL Chile CM Cameroon CO Colombia CR Costa Rica CV Cape Verde CW Curaçao CY Cyprus CZ Czech Republic DE Germany DJ Djibouti DK Denmark DM Dominica DO Dominican Republic DZ Algeria EC Ecuador EG Egypt ES Spain ET Ethiopia FI Finland FJ Fiji FK Falkland Islands (Malvinas) FM Micronesia, Federated States of FO Faroe Islands FR France GA Gabon GB United Kingdom GD Grenada GE Georgia GF French Guiana GG Guernsey GH Ghana GI Gibraltar GL Greenland GM Gambia GP Guadeloupe GQ Equatorial Guinea GR Greece GT Guatemala GY Guyana HK Hong Kong, SAR China HN Honduras HR Croatia HT Haiti HU Hungary ID Indonesia IE Ireland IL Israel IM Isle of Man IN India IQ Iraq IT Italy JE Jersey JM Jamaica JO Jordan JP Japan KE Kenya KG Kyrgyzstan KH Cambodia KM Comoros KN Saint Kitts and Nevis KR Korea (South) KW Kuwait KY Cayman Islands KZ Kazakhstan LA Lao PDR LB Lebanon LC Saint Lucia LI Liechtenstein LK Sri Lanka LS Lesotho LT Lithuania LU Luxembourg LV Latvia LY Libya MA Morocco MD Moldova ME Montenegro MF Saint-Martin (French part) MG Madagascar MK Macedonia, Republic of MM Myanmar MN Mongolia MO Macao, SAR China MS Montserrat MT Malta MU Mauritius MW Malawi MX Mexico MY Malaysia MZ Mozambique NA Namibia NC New Caledonia NE Niger NF Norfolk Island NG Nigeria NI Nicaragua NL Netherlands NO Norway NP Nepal NZ New Zealand OM Oman PA Panama PE Peru PG Papua New Guinea PH Philippines PK Pakistan PL Poland PM Saint Pierre and Miquelon PR Puerto Rico PS Palestinian Territory PT Portugal PY Paraguay QA Qatar RE Réunion RO Romania RS Serbia RU Russian Federation RW Rwanda SA Saudi Arabia SC Seychelles SD Sudan SE Sweden SG Singapore SH Saint Helena SI Slovenia SK Slovakia SL Sierra Leone SN Senegal SR Suriname ST Sao Tome and Principe SV El Salvador SY Syrian Arab Republic (Syria) SZ Swaziland TC Turks and Caicos Islands TG Togo TH Thailand TL Timor-Leste TM Turkmenistan TO Tonga TR Turkey TT Trinidad and Tobago TW Taiwan, Republic of China TZ Tanzania, United Republic of UA Ukraine UG Uganda US United States of America UY Uruguay UZ Uzbekistan VC Saint Vincent and Grenadines VE Venezuela (Bolivarian Republic) VG British Virgin Islands VI Virgin Islands, US VN Viet Nam WS Samoa YE Yemen YT Mayotte ZA South Africa ZM Zambia ZW Zimbabwe
Yes. India should be supported. But keep in mind that not all networks reliably deliver "Firebase verification messages."