<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2021-01-15</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0001412408</issuerCik>
        <issuerName>Phreesia, Inc.</issuerName>
        <issuerTradingSymbol>PHR</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001564521</rptOwnerCik>
            <rptOwnerName>Hoffman Allison C</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O PHREESIA, INC.</rptOwnerStreet1>
            <rptOwnerStreet2>424 FAYETTEVILLE ST., SUITE 1400</rptOwnerStreet2>
            <rptOwnerCity>RALEIGH</rptOwnerCity>
            <rptOwnerState>NC</rptOwnerState>
            <rptOwnerZipCode>27601</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>General Counsel &amp; Secretary</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2021-01-15</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>19059</value>
                    <footnoteId id="F1"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0.00</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>86467</value>
                    <footnoteId id="F2"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">The shares reported in this transaction represent Restricted Stock Units (&quot;RSUs&quot;) issued under the Phreesia, Inc. 2019 Stock Option and Incentive Plan. Each RSU represents the contingent right to receive one share of the Issuer's common stock. The RSUs vest as follows: 10% of the RSUs shall vest on January 15, 2022, 20% of the RSUs shall vest on January 15, 2023, 30% of the RSUs shall vest on January 15, 2024 and 40% of the RSUs shall vest on January 15, 2025, subject to the Reporting Person's continued service to the Issuer through each vesting date.</footnote>
        <footnote id="F2">A portion of these shares represent RSUs. Each RSU respesents a contingent right to receive one share of the Issuer's common stock.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/ Allison C. Hoffman</signatureName>
        <signatureDate>2021-01-20</signatureDate>
    </ownerSignature>
</ownershipDocument>
