diff --git a/backend/src/main/java/com/srsystem/exception/ErrorCode.java b/backend/src/main/java/com/srsystem/exception/ErrorCode.java
index d9cf3bb..0e86c05 100644
--- a/backend/src/main/java/com/srsystem/exception/ErrorCode.java
+++ b/backend/src/main/java/com/srsystem/exception/ErrorCode.java
@@ -27,7 +27,8 @@ public enum ErrorCode {
     DUPLICATE_GROUP_CODE(HttpStatus.CONFLICT, "COD_ERR_002", "이미 존재하는 그룹 코드입니다"),
     GROUP_HAS_CODES(HttpStatus.BAD_REQUEST, "COD_ERR_003", "그룹에 속한 코드가 있어 삭제할 수 없습니다"),
     PLAN_NOT_FOUND(HttpStatus.NOT_FOUND, "PLN_ERR_001", "주간 계획을 찾을 수 없습니다"),
-    INVALID_STATUS(HttpStatus.BAD_REQUEST, "TCK_ERR_004", "처리할 수 없는 상태입니다");
+    INVALID_STATUS(HttpStatus.BAD_REQUEST, "TCK_ERR_004", "처리할 수 없는 상태입니다"),
+    INVALID_INPUT_VALUE(HttpStatus.BAD_REQUEST, "SYS_ERR_002", "필수 입력값이 누락되었거나 올바르지 않습니다");
 
     private final HttpStatus httpStatus;
     private final String errorCode;
diff --git a/backend/src/main/java/com/srsystem/service/EmployeeService.java b/backend/src/main/java/com/srsystem/service/EmployeeService.java
index ab006d1..f514e58 100644
--- a/backend/src/main/java/com/srsystem/service/EmployeeService.java
+++ b/backend/src/main/java/com/srsystem/service/EmployeeService.java
@@ -83,14 +83,24 @@ public class EmployeeService {
 
     @Transactional
     public Employee create(Employee employee) {
-        if (employee.getEmail() != null && employeeRepository.findByEmail(employee.getEmail()).isPresent()) {
+        if (employee.getLoginId() == null || employee.getLoginId().isBlank()) {
+            throw new BusinessException(ErrorCode.INVALID_INPUT_VALUE);
+        }
+        if (employeeRepository.findByLoginId(employee.getLoginId()).isPresent()) {
+            throw new BusinessException(ErrorCode.DUPLICATE_LOGIN_ID);
+        }
+        if (employee.getEmail() != null && !employee.getEmail().isBlank() && employeeRepository.findByEmail(employee.getEmail()).isPresent()) {
             throw new BusinessException(ErrorCode.DUPLICATE_LOGIN_ID);
         }
         if (employee.getRoleCode() == null) employee.setRoleCode(RoleCode.EMPLOYEE);
         if (employee.getEmpStatus() == null) employee.setEmpStatus(EmpStatus.ACTIVE);
         if (employee.getDispatchStatus() == null) employee.setDispatchStatus(DispatchStatus.WAITING);
 
-        employee.setPassword(passwordEncoder.encode(employee.getPassword()));
+        String rawPassword = employee.getPassword();
+        if (rawPassword == null || rawPassword.isBlank()) {
+            rawPassword = "admin123";
+        }
+        employee.setPassword(passwordEncoder.encode(rawPassword));
         try {
             return employeeRepository.save(employee);
         } catch (DataIntegrityViolationException e) {
diff --git a/backend/src/main/java/com/srsystem/util/PhoneEncryptionConverter.java b/backend/src/main/java/com/srsystem/util/PhoneEncryptionConverter.java
index a8fb59f..ce2011c 100644
--- a/backend/src/main/java/com/srsystem/util/PhoneEncryptionConverter.java
+++ b/backend/src/main/java/com/srsystem/util/PhoneEncryptionConverter.java
@@ -24,7 +24,20 @@ public class PhoneEncryptionConverter implements AttributeConverter<String, Stri
     private SecretKey secretKey;
     private final SecureRandom secureRandom = new SecureRandom();
 
-    public PhoneEncryptionConverter(@Value("${app.encryption.phone-key}") String key) {
+    private static final String DEFAULT_KEY = "0123456789abcdef0123456789abcdef";
+
+    public PhoneEncryptionConverter() {
+        this(DEFAULT_KEY);
+    }
+
+    public PhoneEncryptionConverter(@Value("${app.encryption.phone-key:0123456789abcdef0123456789abcdef}") String key) {
+        if (key == null || key.isBlank()) {
+            key = DEFAULT_KEY;
+        }
+        initKey(key);
+    }
+
+    private void initKey(String key) {
         byte[] keyBytes = key.getBytes();
         if (keyBytes.length < 16) {
             byte[] padded = new byte[16];