This is even more straight forward to do using the row_number function and set the order to select Current first if it exists, here is a quick sample

😎

USE tempdb;

GO

SET NOCOUNT ON;

GO

DECLARE @TXML XML = N'

<Persons>

<Person ID="776">

<EmailAddress>abc@abc.com</EmailAddress>

<NotifyElectronically>0</NotifyElectronically>

<InactiveAttorney>false</InactiveAttorney>

<PhoneNumber>127</PhoneNumber>

<PhoneNumber Current="true">258</PhoneNumber>

<PhoneNumber>123</PhoneNumber>

<HouseNumber>369</HouseNumber>

</Person>

<Person ID="777">

<EmailAddress>abcd@abc.com</EmailAddress>

<NotifyElectronically>0</NotifyElectronically>

<InactiveAttorney>false</InactiveAttorney>

<PhoneNumber>123</PhoneNumber>

<PhoneNumber>393</PhoneNumber>

<HouseNumber>369</HouseNumber>

</Person>

</Persons>

';

;WITH BASE_DATA AS

(

SELECT

PERSON.DATA.value('@ID','INT') AS ID

,ROW_NUMBER() OVER

(

PARTITION BY PERSON.DATA.value('@ID','INT')

ORDER BY ISNULL(PHONE.DATA.value('@Current','VARCHAR(10)'),'0') DESC

) AS PHONE_RID

,PERSON.DATA.value('EmailAddress[1]','VARCHAR(100)') AS EmailAddress

,PERSON.DATA.value('NotifyElectronically[1]','TINYINT') AS NotifyElectronically

,PHONE.DATA.value('../PhoneNumber[1]','VARCHAR(25)') AS PhoneNumber

,PHONE.DATA.value('@Current','VARCHAR(10)') AS [Current]

FROM @TXML.nodes('Persons/Person') AS PERSON(DATA)

OUTER APPLY PERSON.DATA.nodes('PhoneNumber') AS PHONE(DATA)

)

SELECT

BD.ID

,BD.EmailAddress

,BD.NotifyElectronically

,BD.PhoneNumber

,ISNULL(BD.[Current],'false') AS [Current]

FROM BASE_DATA BD

WHERE BD.PHONE_RID = 1;

Results

ID EmailAddress NotifyElectronically PhoneNumber Current

---- -------------- -------------------- ------------ --------

776 abc@abc.com 0 127 true

777 abcD@abd.com 0 123 false